154 INTERNAL COMBUSTION ENGINE [CHAP.V

Iff,

(2) Reduce the amount of fuel used per cycle, leaving the air

supply untouched; or

(3) Reduce the amount of both fuel and aii keeping the pro-

portion of fuel to air the same; or

(4) Cause the ignition to come later, or he cut off altogether.
101. Hit and Miss Governing. — The first of these alterna-

tives is knomi as " hit-and-miss " governing, because when

the speed gets too high the governor lever is made to lift up a

piece of metal which lies between, the gas valve tappet

the valve stem. This is shewn in Fig. 47. B is the piece

of in question. When the cam E pushes the roller Gr

it makes the tappet rod
GDC, which is pivoted at
D, push the valve A open.
(The valve A is the gas
admission valve ; after
the gas passes this valve
it joins the air supply,
and both pass through a
larger valve, which opens
a little earlier, into the
cylinder. ) This could not
be done if B were not In
line between C and A as
shown. The governor
lever lifts B out of this
line when the speed is too
high, and the valve A is

consequently not opened and no gas reaches the cylinder,
TMs reduces the engine speed until the governor again inserts
the pieoe B. The engine speed wiH therefore be kept steady
at aH loads up to the marimum load the engine can take.
The effect of hit and miss governing is clearly shown on
the indicator diagram. In Fig. 48 is shown, such a diagram
taken during two successive strokes of an engine. The " Mt "
or working stroke .is shown at "ACD,. and the c< miss " or idle
is shown at AS.- The compression line of '"miss "
lies Wow that" of tie *c hit.'* TMs is because the gas
oa the suction stroke and the air valve" acting '

FIG. 47.—Diagram illustrating "Hit-

Mechanism.

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